Agriculture is a multibillion dollar, international industry. One area of importance is the production of fruits by cultivating flowering plants. Citrus, characterized by plants that produce fragrant flowers and edible juicy fruits such as oranges, grapefruits, lemons, and tangerines, is a common term and genus of flowering plants in the rue family. Cultivating and the production of commercial citrus products play an important role in the economies of many countries. For example, Florida's citrus industry is a multibillion dollar industry employing tens of thousands of jobs. While Florida's orange industry has weathered hardships associated with canker disease, hurricanes, and hard freezes, the industry has faced its toughest challenge recently with the introduction of a bacterial disease known as citrus greening.
Huanglongbing (HLB), or citrus greening disease, is a plant based disease spread by the Asian citrus psyllid, Diaphorina citri Kuwayama and Trioza erytreae. It was first reported in China in the early 1900s, but has spread to many citrus producing regions. HLB is caused by a phloem-limited bacterial pathogen, Candidatus Liberibacter. The bacterial pathogen plugs the phloem (plant's vasculature tissue), thereby limiting nutrient movement. Once infected, the citrus plant eventually produces inedible fruits. Early symptoms of the disease include yellowing of the leaves on an individual limb or in sections of the tree. The leaves that turn yellow have asymmetrical patterns of blotchy yellowing, or molting of the leaf. As the disease progresses, the fruit size becomes smaller and the juice turns bitter. Eventually, the fruit becomes lopsided, has dark aborted seeds, and tends to drop prematurely. There is presently no known cure for plants infected with HLB. Applying foliage nutrients provides temporary delay of various symptoms of the infection. However, the bacteria remain alive and active, resulting in the decline in usable fruit production. Introduction of antibiotics into the tree's vasculature systems via injections is not viable as such substances tend to be toxic. Moreover, surface applied copper compounds are not sufficient to inhibit bacterial activity within the xylem and phloem of the plant. As such, current HLB strategies include insecticide sprays to limit the populations of the psyllid or the removal of infected plants and repopulation. Such methods, however, are time consuming, costly, and fail to prevent new plants from becoming infected.
Accordingly, there is a need in the art for an effective composition, and method of using the composition, to treat diseases associated with flowering plants, such as citrus plants.